Improvement in achromatic lenses



Lens. y

Patentedi Sept.. 27, 1864..-

JULIA A. w. riirz, or

Specification forming part of Letters Patent No. 4;.1886?, dnte'd September 27, 1864; antednted September To all .uhom it may concern Be it known that HENRY FITZ, of New York, in the county of New York, in the State of New York, lately deceased, did invent au improved method of constructing Lenses for Photographic and Optical Instruments, Cameras, &c.; and I, JULIA A. W. Frrz, executrixof the said HENRY Frrz, do hereby declare that the following is a full and exact description thereof, reference being had to the accompanying drawing and to the letters of reference marked thereon. Said drawing shows a section of the lenses as corrected and arranged for use in a camera-tube, and in Which- A is the exterior front pla n9 onvex lens of crown glass. B is the interior front planoconcave lens of flint glass. C is the interior back plano-concave lens of flint glass, and D is the exterior back plwonvex lens of crown glass.

'lhe nature of said invention consists in making the corrections for achromatic and spherical aberrations by employing lenses with the outer surfaces so curved and com bined as to admit of .the use of plane surfaces in the place of what are technically termed the. interior correcting curves, and by making the interior surfaces plane.

To enable others skilled in the art to make and use the said invention, 1 will proceed to describe its construction and operation.

The lenses are made and arranged as shown in the drawingthat is to say, the front lens (or lens toward the object) is composed of a plano-convex leus, A, of crown glass, of any required power or size, and is corrected by a plano-concave lens, B, of tlint glass, the curve for the concave lens being more flat STATES NEW YORK, N. Y., ADMINISTRATRIX oF 0F HENRY Fl'rz, DECEASED. A

PATENTv Oirrrcr.n

"iM'PaoyEMENT IN AoHaoMATIc LENsEs.

than the curve ot' the convex lens. The back or inner lens is composed of a plano-convex lens, D, of crown glass, of greater convexly,

than A, aud of a plano-concave lens` 0,0t'

tliut glass, more concave than B. These lenses being properly cemented ou theirl plane surfaces, and arranged as shown, are employed in a camera in the usual manner for copyn o r taking landscapes, or they are errang f for use in microscopes or other optical instruments. t

Heretofore all achromaticnstruments have been made with concave and convex surfaces, matched and cemented together, or with what isknowu to the art as interior correcting curves, whereas by the above invention the interior or cemented surfaces are plane, 'and can be made at a greatly reduced expense. By this arrangement, also, all the advantages of short focal length, large and flat field, and freedom from distortion, claimed for the spherical or globnlarlens, are attained with greater facility and cheapuess than by that instru. ment. The sperical aberrations are thoroughly corrected, and the defect called the ghost is completely dispelled.

'What I claim as the above invention, and desire to secure by Letters Patent, is-

The method of correcting spherical and achromatic aberrations and curvatures of eld in cameras for taking photographic views audfor the various optical instruments, substantially as specied and set forth.

JULIA A. W. FITZ,

THE ESTATE 

